The present invention relates to a device for controlling an oiled air compressor, which is included in a compressed-air system for a motor vehicle and which is driven by the engine of the motor vehicle and supplies compressed air to at least one consumer in the compressed-air system, a control unit being provided for controlling the function of the air compressor by activating the air compressor at a lower predetermined pressure level for charging the compressed-air system and deactivating the same at a higher predetermined pressure level for relieving the air compressor. The invention also relates to a method for controlling an oiled air compressor, which is included in a compressed-air system for a motor vehicle and which is driven by the engine of the motor vehicle and supplies compressed air to at least one consumer in the compressed-air system, the function of said air compressor being controlled by being activated at a lower predetermined pressure level for charging the compressed-air system and deactivated at a higher predetermined pressure level for relieving the air compressor.
In motor vehicles, in particular heavy goods vehicles, the internal combustion engine of the vehicle is normally used also to drive such auxiliary appliances as generators and air compressors. As to air compressors, they are lubricated with oil and in most cases of piston type. They are part of compressed-air systems for supplying various consumers, such as brakes and air suspension, in the vehicle with compressed air. The supply of lubricating oil to the air compressor is often connected with the internal combustion engine, such that the same lubricating oil is used for both.
For a long time, problems have arisen owing to lubricating oil from the air compressor being entrained into the system by the generated compressed air. The entrained lubricating oil is present in liquid as well as evaporated form and causes problems in the brakes, the air suspension etc, in the form of general messiness and swelling/degradation of primarily rubber packings.
Since the air compressor is driven by the internal combustion engine all the time and thus rotates constantly, whereas the generation of compressed air or charging is needed about 20-50% of the time, a system for controlling the charging is wanted. This may be achieved by means of a control unit, for instance a regulator, which activates the air compressor at a lower minimum pressure in the order of say 7.5 bar and deactivates the same at a higher maximum pressure in the order of say 12.5 bar.
The deactivation may be achieved by relieving the air compressor. Preferably, this is carried out by preventing the air compressor from charging air by blocking its outlet. The blocking may be provided by a shut-off device in the form of a stop valve or the like, which is controllable by the control unit. This means that the air compressor, which is still rotating, accumulates the lubricating oil which is needed for the lubrication of the compressor pistons and blows past the piston rings during the entire deactivation phase, that is until the renewed activation at the minimum pressure.
When the air compressor is activated and starts charging the compressed-air system by generating compressed air, the stored lubricating oil in liquid and evaporated form is entrained by the compressed air into the system. This is also the case of condensate and other pollutants which may have formed during the deactivation phase in the compressor cylinders by the relieving of pressure/cooling. If a dryer is also arranged in conventional manner downstream of the air compressor in the compressed-air system, a portion of the pollutants is captured by the air dryer. However, above all the evaporated portion of the lubricating oil passes the air dryer and is then precipitated/condensed in the brakes and the air suspension etc, causing the above-mentioned damage.
It is true that pollution of the above-described type also occurs when the air compressor is activated and generates compressed air. The total amount of pollutants is, however, completely decisive of how fast the problem arises.
In order to solve this problem to some extent, a so-called line onloader-system may be used. This means that the air compressor generates compressed air constantly and that excess air, when deactivating, is exhausted to atmosphere via a valve or the like, which can be provided in the air dryer. A great problem of this method is the high fuel consumption of the internal combustion engine. For instance, when driving 200,000 km, use is made of about 1000 l more fuel a year than in the case where the air compressor is deactivated.
An object of the present invention is to make it possible to apply an inexpensive, space-saving and efficient solution to the problem of pollution in the compressed air after the deactivation phase in the air compressor.
This object is achieved by a device of the type defined by way of introduction by means of a drainage unit, which in connection with the activation of the air compressor drains pollutants, which have accumulated in the air compressor during the deactivation, before the air compressor is allowed to start charging the compressed-air system. In the method according to the invention, the object is achieved by draining, in connection with the activation of the air compressor, pollutants which have accumulated in the air compressor during the deactivation, before the air compressor starts charging the compressed-air system.